56 TEXT-BOOK OF BACTERIOLOGY. 



to make them anhydrous, then into oil of cloves or cedar to make 

 them transparent, and lastly into Canada balsam, one drop of 

 which, in the centre of a glass slide, is sufficient for a moderately 

 large section. The removal of a section from one solution to an- 

 other is best managed with a needle and a metal spatula, to bear 

 the out-spread slice of tissue. 



Others, following the plan of Weigert, perform the whole stain- 

 ing process from the beginning on the slide, thus avoiding the 

 necessity of transporting the section. This plan has undeniable 

 iad vantages for many cases; the sections do not fold or roll up, do 

 not tear so often, and require very much less time for their treat- 

 ment. Lay the section on a slide, pour the staining fluid upon it, 

 pour it off again after staining, rinse it thoroughly, first with di- 

 luted acetic acid and then with distilled water, remove traces of 

 water by alcohol, let a few drops of oil of cedar or oil of cloves fall 

 upon it, remove excess of oil with blotting-paper, and inclose it in 

 Canada balsam. 



As to the choice of a stain in particular cases, either the simple 

 or the compound fluids can be used; for example, either Loffler's 

 methyl-blue or Ziehl's carbol-fuchsin, etc. 



The time during which the preparation should be exposed to 

 the action of the various stains 'depends upon circumstances; in 

 fact, the range of time over which practical experiments have been 

 made extends from a few seconds up to forty-eight hours. 



If the bleaching power of water is not sufficient it is replaced by 

 alcohol, and if this is still insufficient, strong acids — muriatic, sul- 

 phuric, or nitric— are added to the water or alcohol. The coloring 

 matter then disappears almost entirely from the connective tissues, 

 but it is also apt to be washed out of the nuclei and bacteria, and 

 these strong decoloring agents should only be resorted to in ex- 

 ceptional cases. 



The methods above described will be generally successful, but 

 they fail occasionally, especially when a tissue contains bacteria 

 which receive the stain without difficulty, but lose it again with 

 equal readiness when bleaching. 



A particularly dangerous rock for these sensitive micro-organ- 

 isms is the alcohol treatment to which the sections must be sub- 

 mitted before they can be transferred to the oil which is to clarify 

 them. 



It is known that alcohol is not only a means for removing water, 

 but also a very efficacious decoloring or bleaching agent, and this 

 latter quality often shows itself to a very undesirable degree. 

 Various attempts have been made to overcome this difficulty, and 



